Legionella pneumophila
Introduction Legionella pneumophila (L. pneumophila) is an obligately aerobic gram-negative bacterium. Legionella is the only genus within the wider Legionellaceae family , with L. pneumophila being the most common species containing 15 serotypes (Brady and Sundareshan, 2019) . The full classification can be found here (Links to an external site.) . Legionella is a fastidious bacterium requiring L-cysteine and iron to be added to minimal media for it to be grown. It’s a facultative intracellular pathogen that that is opportunistic in humans and causes Legionellosis. Legionellosis can be observed as Pontiac fever, Lochgoilhead fever ( both are less severe) or the Pneumonia like infection Legionnaires' disease if it enters the human lungs. It’s a Coccobacilli that remains between 0.3-0.9μm in width & 2-20μm in length this can be seen in Figure 1. However, it’s pleomorphic so its form does vary slightly, which can be seen in Figure 2 (Diederen, 2007). The bacterium is also motile with a single flagellum responsible for its motion. (Baron, 1996). Legionella stains poorly in the Gram test and gives a positive result with Giemsa stain (Reference). L. pneumophila is found in freshwater sources such as rivers, lakes and reservoirs. It survives and proliferates in temperatures between 20-45°C . It poses a threat to humans when it grows to large numbers in places such as shower heads, hot tubs, water tanks and general plumbing systems. (USA. Department of Health & Human Services. CDC, 2018-a). To cause infection, small water droplets containing the bacterium must be inhaled into the lungs, therefore it is unlikely that infection will occur from drinking contaminated water. L.pneumophila are normally only found in small numbers so they don't pose a threat to humans. Identifying ''Legionella pneumophila'' Variuos techniques can be used to identify L.pneumophila. Samples from urine, sputum, blood, respiratory secretions or other bodily fluids are typically tested for bacteria. A Urinary Antigen Test (UAT) could be performed to identify the lead cause of Legionellosis from urine samples via detection of antibodies from the L. pneumophila serogroup 1 (Lp1). This is one of the most commonly used laboratory test. All serogroups & species of Legionella are potentially pathogenic ,so a negative result in the UAT should be confirmed by a second test using culturing of Legionella on Buffered Charcoal Yeast Extract (BCYE) agar with Iron and Cysteine. Colonies exhibit a yellow pigment when viewed under a long-wave UV light (360 nm ± 20nm). This technique allows all species of Legionella to be detected ( unlike the urinary antigen test) but requires precise temperatures and timing during the heat and acid treatment before culturing. Variability in results are common due to the subjective interpretation of scientists. As a final confirmatory test, the suspected L.pneumophila species are plated on different media which are limiting for certain factors e.g Nitrogen (USA. Department of Health & Human Services. CDC, 2018-b). Alternatively, polymerase chain reaction (PCR) for DNA amplification can be used. However, living and dead cells are difficult to tell apart and it is possible that a positive result is obtained even though no viable bacteria are present. (AACC Lab Tests Online, 2018) Legiolert is a test that exclusively detects L.pneumophilia. Live cells are cultured and if L.pneumphila is present then a colour change is observed. Serotyping of cultured L.pneumophila can also be performed and consists of techniques such as the latex agglutination screening test, the indirect fluorescent antibody (IFA) test and enzyme immunoassays (EIA). Details of these techniques can be found here (Links to an external site.) (Broder, 2017). Mechanisms of ''Legionella pneumophila'' infection